Fix MCP error wrapping for DRC payloads

tests/test_mcp_error_wrapping_static.py

@@ -0,0 +1,51 @@
+"""
+Regression tests for MCP error wrapping in TypeScript tool adapters.
+
+KiCad backend commands may report domain failures as JSON payloads such as
+{"success": false, "message": "No board is loaded"}. The MCP tool result must
+also be marked with isError so clients do not treat the failed command as OK.
+"""
+
+from pathlib import Path
+
+import pytest
+
+ROOT = Path(__file__).parent.parent
+TOOLS_DIR = ROOT / "src" / "tools"
+DESIGN_RULES_TS = TOOLS_DIR / "design-rules.ts"
+TOOL_RESPONSE_TS = TOOLS_DIR / "tool-response.ts"
+
+
+@pytest.mark.unit
+class TestMcpErrorWrapping:
+    def test_helper_marks_only_explicit_failure_payloads_as_mcp_errors(self):
+        """A KiCad success:false payload must become an MCP isError result."""
+        helper = TOOL_RESPONSE_TS.read_text(encoding="utf-8")
+
+        assert "export function formatKicadResult" in helper
+        assert "success === false" in helper
+        assert "isError: true" in helper
+
+    def test_design_rule_tools_use_shared_error_wrapper(self):
+        """DRC/design-rule wrappers must not return success:false as a plain OK result."""
+        source = DESIGN_RULES_TS.read_text(encoding="utf-8")
+
+        assert 'import { formatKicadResult } from "./tool-response.js";' in source
+
+        for command in (
+            "set_design_rules",
+            "get_design_rules",
+            "run_drc",
+            "add_net_class",
+            "assign_net_to_class",
+            "set_layer_constraints",
+            "check_clearance",
+            "get_drc_violations",
+        ):
+            marker = f'callKicadScript("{command}"'
+            command_index = source.find(marker)
+            assert command_index != -1, f"{command} wrapper not found"
+
+            next_tool_index = source.find("server.tool(", command_index + len(marker))
+            wrapper_body = source[command_index : next_tool_index if next_tool_index != -1 else None]
+            assert "return formatKicadResult(result);" in wrapper_body